Exposure to particulate matter and other contaminates such as ozone can damage delicate lung tissue. For this reason, medical studies recommend that people breathe filtered air when the air quality is poor. This is particularly true during physical exercise when the lungs not only process greater amounts of air, but also expand to a greater extent, thus allowing contaminates to penetrate further into lung tissue. To prevent such exposure, medical and air quality professionals recommend cessation of exercise while exposed to poor air quality.
Air quality problems are dramatically worse near roadways where vehicles operate. Vehicles not only create and stir up particulate matter in the air, but also introduce contaminates such as carbon monoxide, various hydrocarbons, and oxides of nitrogen, all of which are both unhealthy and contribute to the formation of ozone. Ozone has been shown to lead to a variety of lung conditions in humans including asthma, reduction in lung function, and even premature death. Since bicyclists, joggers, and walkers often utilize vehicle roadways, they are especially prone to unhealthy exposures to each of these pollutants, even when overall air quality is otherwise within acceptable limits.
It is not necessary that all poor-quality air be filtered in order to ensure that the air quality is safe to breathe. Rather, diluting unfiltered air with sufficient filtered air will bring the air quality within acceptable limits.
Properly filtered air allows people to exercise safely even when ambient air quality is poor, however existing air filtration systems are not suited to all circumstances. Many existing systems are not portable. Systems that are portable usually require obstruction of the nose or mouth passage with a mask or a mouthpiece. These limitations can prevent not only unobstructed breathing, but also talking and the consumption of food and water while the systems are in place. For people engaged in activities such as walking, jogging, or bicycling, these limitations make use of the existing air filtration devices undesirable.
One consequence of the existing filtration limitations is that people who would otherwise commute on bicycles will drive vehicles on poor air quality days when automobile use is discouraged, thus exacerbating the already poor quality of the air.